The study analyses the distribution of productivity of authors in theoretical population genetics (TPG) as reflected in their publication output from 1881 to 1980 from two different approaches. The internal dynamics of TPG specialty affecting the distribution of the productivity of authors is studied using time cross-sectional type of approach. Here the productivity distribution of authors in 10 time-year blocks and in three phases of the development (1921-50, 1951-65 and 1966-80) of TPG is studied using cohort type of approach. The extent of cumulative advantage acquired by the prolific group of authors over time in TPG is also studied. The paper also analyzes the regularity in the distribution of productivity of various cohorts, having same length of activity, but different periods of participation.